Cayman 27 – ARCHIVE

An inside look at the reverse osmosis process

Before any water can be delivered from pipelines to your faucets, it needs to be made potable through the process of reverse osmosis.

Water Authority Cayman has four reverse osmosis plants on Grand Cayman.

“Basically what we do is separate the salt and the water, and we get rid of the concentrated salt, and we get fresh water on the other side,” said Graduate Engineer Ahmed Elsheshtawy.

He told Cayman 27 more than four million gallons of groundwater are drawn into the system every day from 150 foot deep induction wells. It’ s filtered one more time before it enters the RO plant.

“In order for the RO membranes to work, we need the water to be pressurized at a very high pressures and that’s why we use high pressure pumps that can put the water up to 750 psi, which is very very high pressure,” said Mr. Elsheshtawy.

After the salt has been removed, the water is treated further.

“After it comes out of the membranes, we need to remove hydrogen sulfide, which is a gas found in the water. We use a degasifier and the gas scrubber to do that. After that we add some chemicals to the water to make sure that everything is perfectly high quality for the potable water,” said Mr. Elsheshtawy.

Mr. Elsheshtawy said Cayman Water Authority has more capacity than it needs to supply the island with water, even with one plant offline for renovations.

“The Lower Valley plant is not operational at this time, there is some renovation going on there, but we can still produce enough water for all our customers, and that’s a good thing. When we have these plants, we always have more than what we actually need in case any shutdowns or renovation work needs to be done,” said Mr. Elsheshtawy.

He said the water goes through rigorous testing daily before it’s sent through the pipes.

Water Authority Cayman told Cayman 27 the US is finally catching on to reverse osmosis. California is now building what will be the largest RO plant in the western hemisphere.

About the author

Joe Avary

Joe Avary

Joe Avary has been with Cayman 27 since 2014. He brings 20 years in television experience to the job, working hard every day to bring the people of Cayman stories that inform the public and make a difference in the community. Joe hopes his love for the Cayman Islands shines through in his informative and entertaining weather reports. If you have a story idea for Joe or just want to say hello, call him at 324-2141 or send an email to

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